The great advances made over the last few years in the identification of signalling molecules that pattern the limb bud along the three axes make the limb an excellent model system with which to study developmental mechanisms in vertebrates. The understanding of the signalling networks and their mutual interactions during limb development requires the characterisation of the corresponding downstream genes. In this study we report the expression pattern of Slug, a zinc-finger-containing gene of the snail family, during the development of the limb, and its regulation by distinct axial signalling systems. Slug expression is highly dynamic, and at different stages of limb development can be correlated with the zone of polarizing activity, the progress zone and the interdigital areas. We show that the maintenance of its expression is dependent on signals from the apical ectodermal ridge and independent of Sonic Hedgehog. We also report that, in the interdigit, apoptotic cells lie outside of the domains of Slug expression. The correlation of Slug expression with areas of undifferentiated mesenchyme at stages of tissue differentiation is consistent with its role in early development, in maintaining the mesenchymal phenotype and repressing differentiation processes. We suggest that Slug is involved in the epithelial-mesenchymal interactions that lead to the maintenance of the progress zone.